updated 12:41 pm EST, Thu February 27, 2014

The British security intelligence agency GCHQ secured millions of photographs from webcams used with Yahoo's chat services, a report alleges. The agency is claimed to have captured and stored images from more than 1.8 million users in one six month period in 2008 alone, with the surveillance activities said to have continued from 2008 to 2010, though it is possible the program continued for years afterward.

Documents revealed byThe Guardian state that collection and storage of Yahoo webcam chats, under a program called "Optic Nerve," was done regardless of whether or not those pictured were an intelligence target. Rather than collect videos of chats, the program collected an image from each web cam every five minutes. GCHQ is said to have trialled automatic facial recognition searches on the images, in order to try and find known persons of interest. One document apparently showed this functionality was "now closed... but shortly to return!".

It is said that GCHQ lacked the ability to exclude images of US or UK citizens from storage, and has no legal compulsion in the UK to remove or delete data relating to the country's citizens, but that "additional legal authorizations" were needed before searching for individuals located in the UK at that time.

The report notes that a large amount of images taken from Yahoo at the time were pornographic in nature, with estimates suggesting such images made up between 3 percent and 11 percent of pictures harvested. The document also notes that the asymmetric nature of Yahoo webcam chat, namely allowing multiple people to watch one stream without a reciprocal video stream being required, allowed it "to be used for broadcasting pornography." Despite the nudity, GCHQ apparently attempted to keep the image archive clean for analysts, though the automated "pornography detectors" would often incorrectly tag a person's face as such material, just from the percentage of the screen made up of skin tones.

Section of leaked documents concerning Yahoo webcam chat content

The amount of data available to GCHQ via Yahoo is unknown, as it is not clear if images collected were for public-only chats, or if it took into account private conversations as well. Yahoo was also not the only source of images GCHQ considered, as one document showed it was looking into the possible use of the Xbox 360's Kinect camera.

A spokesperson for GCHQ told the report it is a "longstanding policy" that it does not comment on "intelligence matters," and that all of what GCHQ performs "is carried out in accordance with a strict legal and policy framework," with oversight from the secretary of state, the interception and intelligence services commissioners, and the Parliamentary Intelligence and Security Committee.

Yahoo claimed it was not aware of the activity and would not have condoned it in the first place. A statement from the company claims "This report, if true, represents a whole new level of violation of our users' privacy that is completely unacceptable, and we strongly call on the world's governments to reform surveillance law consistent with the principles we outlined in December."

The Yahoo webcam chat report is the latest in a string of revelations concerning the surveillance activities of security agencies, such as GCHQ and the NSA, first started by whistle-blower Edward Snowden.